Invisible damage identification and danger warning for steel box girders using the metal magnetic memory method

Abstract

Locating invisible damage and detecting the critical stress state leading to structural damage or failure are essential tasks in structural diagnosis. In this study, a four-point bending static loading experiment was conducted on two steel box girder members—one nondestructive, whereas the other had a butt weld—based on the metal magnetic memory (MMM) method. The correlation between the buckling failure position of the steel box girders and distribution characteristics of the magnetic signals was analyzed. The critical stress states of the elastic and elastic–plastic or elastic–plastic and plastic stages were statistically described using characteristic magnetic parameters. The results showed that the extremum position of the magnetic signal variationΔHpywell correlated with the location of the stress concentration. TheΔHpyextremum could locate the invisible damage position and predict the failure position, while the extremum of the average valueΔHpyaand integral value AofΔHpyvalue could accurately diagnose the critical stress state of steel box girders in the elastic and elastic–plastic or elastic–plastic and plastic stages. The proposed magnetic charge model could explain the distribution characteristics of the magnetic signals on the butt weld. These results are expected to provide a basis for effectively evaluating invisible damage using the MMM method.